Spontaneous patterning of confined granular rods

Vertically vibrated rod-shaped granular materials confined to quasi-2D containers self-organize into distinct patterns. We find, consistent with theory and simulation, a density dependent isotropic-nematic transition. Along the walls, rods interact sterically to form a wetting layer. For high rod densities, complex patterns emerge as a result of competition between bulk and boundary alignment. A continuum elastic energy accounting for nematic distortion and local wall anchoring reproduces the structures seen experimentally.     

Probing the Hydrodynamic Behavior of Drug-Induced Tubulin Rings by Fluorescence Correlation Spectroscopy

We describe fluorescence correlation spectroscopy measurements of tubulin polymers composed of tubulin and either of two cytotoxic peptides – dolastatin 10 and cryptophycin 1. These peptides inhibit tubulin polymerization into microtubules, a major component of cellular networks, and instead induce the formation of predominantly single-walled tubulin rings. We determine ratios of the hydrodynamic diameter of dolastatin-tubulin or cryptophycin-tubulin polymers to that of tubulin dimers, which are compared with corresponding ratios calculated for two simple models: 1) a circular ring made with N contiguous spherical beads and 2) a circular ring constructed with N non-spherical monomers, each monomer being represented by 21-minibeads. We find that the computed ratios from the 21-minibead representation agree well with the measured ones when N = 28 and N = 16 for dolastatin-tubulin and cryptophycin-tubulin ring polymers, respectively. That is, the rings are made with 14 and 8 tubulin dimers, confirming the numbers derived by other techniques. The present results further support the applicability of theories that have been developed for calculating hydrodynamic properties of supramolecular biological structures.     

Why do molecules echo atomic periodicity?

Franck–Condon factors are investigated for sequences of free main‐group diatomic molecules. Theory‐based Condon loci (parabolas) and Morse‐potential loci are plotted on Deslandres tables to verify if they, indeed, follow the largest Franck–Condon factors. Then, the inclination angles of the Condon loci are determined. Thus, entire band systems are quantified by one variable, the angle. For all available isoelectronic sequences, this angle increases from a central minimum toward magic‐number molecular boundaries. The theory for the Condon locus gives the angle in terms of the ratio of the upper‐state to the lower‐state force constants. It is concluded that the periodicity is caused due to the fact that this ratio becomes larger as rare‐gas molecules are approached, a trend that probably points to the extreme cases of the rare‐gas molecules themselves. Thus, molecular periodicity echoes atomic periodicity in that data plots have extrema at molecules with magic‐number atoms, yet it does not echo the details of atomic periodicity in series between those molecules. © 2013 The Authors. International Journal of Quantum Chemistry Published by Wiley Periodicals, Inc.     

A reactivity study of addition of organic halides to CpMo(CO)3−: counterion and RX dependences

Rates of reaction of CpMo(CO)₃^? with organic halides to yield CpMo(CO)₃R showed opposite counterion effects according to the type of RX reagent.     

Hydrodynamics of nanoscopic tubulin rings in dilute solutions

We combine fluorescence correlation spectroscopy and sedimentation velocity measurements to probe the hydrodynamic behavior of tubulin dimers and nanoscopic tubulin rings. The rings are rigid, have circular geometry, and are monodisperse in size. We use the high-precision ratio of the sedimentation coefficients and that of the translational diffusion coefficients to validate theories for calculating the hydrodynamic properties of supramolecular structures.     

Bose–Einstein condensation of lithium

7 Li has been studied in a magnetically trapped gas. Many-body quantum theory predicts that the occupation number of the condensate is limited to about 1400 atoms because of the effectively attractive interactions between ⁷Li atoms. Using a versitile phase-contrast imaging technique, we experimentally observe the condensate number to be consistent with this limit. We discuss our measurements, the current theoretical understanding of BEC in a gas with attractive interactions, and future experiments we hope to perform. Received: 4 June 1997